The tribes which Darius proposed to attack occupied the countries north of the Danube. His route, therefore, for the invasion of their territories would lead him through Asia Minor, thence across the Hellespont or the Bosporus into Thrace, and from Thrace across the Danube. It was a distant and dangerous expedition. Darius had a brother named Artabanus. Artabanus was of opinion that the enterprise which the king was contemplating was not only distant and dangerous, but that the country of the Scythians was of so little value that the end to be obtained by success would be wholly inadequate to compensate for the exertions, the costs, and the hazards which he must necessarily incur in the prosecution of it. But Darius was not to be dissuaded. He thanked his brother for his advice, but ordered the preparations for the expedition to go on. He sent emissaries forward, in advance, over the route that his army was destined to take, transmitting orders to the several provinces which were situated on the line of his march to prepare the way for the passage of his troops. Among other preparations, they were to construct a bridge of boats across the Bosporus at Chalcedon. This work was intrusted to the charge and superintendence of an engineer of Samos named Mandrocles. The people of the provinces were also to furnish bodies of troops, both infantry and cavalry, to join the army on its march. The soldiers that were enlisted to go on this remote and dangerous expedition joined the army, as is usual in such cases, some willingly, from love of adventure, or the hope of opportunities for plunder, and for that unbridled indulgence of appetite and passion which soldiers so often look forward to as a part of their reward; others from hard compulsion, being required to leave friends and home, and all that they held dear, under the terror of a stern and despotic edict which they dared not disobey. It was even dangerous to ask for exemption. As an instance of this, it is said that there was a Persian named Oebazus, who had three sons that had been drafted into the army. Oebazus, desirous of not being left wholly alone in his old age, made a request to the king that he would allow one of the sons to remain at home with his father. Darius appeared to receive this petition favorably. He told Oebazus that the request was so very modest and considerate that he would grant more than he asked. He would allow all three of his sons to remain with him. Oebazus retired from the king's presence overjoyed at the thought that his family was not to be separated at all. Darius ordered his guards to kill the three young men, and to send the dead bodies home, with a message to their father that his sons were restored to him, released forever from all obligation to serve the king.